Abstract
We present a theoretical and experimental investigation on refractive index (RI) sensing
characteristics of single mode fiber (SMF) based modal interferometers. Theoretical analysis
reveals that interference between different modes in an SMF has a quite different response to the
RI variation of the external medium. The interference between the core and lower order cladding
modes has negative RI sensitivity whereas that between the core and higher order modes, or between
two different order cladding modes have positive sensitivity. A single-mode-multimode-single-mode
(SMS) fiber Michelson interferometer with a large-core step-index multimode fiber (MMF) is
employed for experimental verification. In the SMS-based Michelson interferometer, the MMF acts as
a mode coupler to excite cladding modes in the SMF. The RI response of the SMS-based structures
with two different lengths of MMF are respectively tested in sodium-chloride water solutions.
Experimental results show excellent agreements with the theoretical analysis.
© 2014 IEEE
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